The detection, treatment and prevention of early childhood eye disease depends to a great extent on a thorough understanding of the mechanisms underlying the growth and development of the human visual system. The specific aims of this research are to study the normal and abnormal visual system of infants and young children using two techniques, one electrophysiological (the visual evoked potential - VEP), the other, psychophysical (forced-choice preferential looking - FPL). First, a series of experiments is proposed to determine why "VEP visual acuity" is better than "FPL visual acuity" in infants and young children. These experiments include: 1) a single trial analysis of the pattern VEP using a two alternative forced-choice psychophysical procedure; 2) a direct comparison of FPL and VEP acuity using counter-phase square wave gratings; and 3) the effect of changes in the luminance, contrast and orientation of grating stimuli on VEP and FPL acuity threshold. A second goal of this research is to determine if it is feasible to use the pattern VEP as a vision screening technique in pre-school children. To achieve this aim, pattern VEPs will be recorded from 1,250 preschool children at 3 day care centers. In addition to VEPs, visual acuity, stereopsis and motility will also be measured. Children who fail any of the tests will receive an ophthalmic examination in our out-patient eye service. The ultimate goal of the screening study will be to determine if the VEP can be used to screen infants and toddlers. The third goal of this research is to directly compare "fast" versions of VEP and FPL techniques in the detection and treatment of amblyopia caused by uniocular congenital cataracts, strabismus, anisometropia, ptosis and lid hemangiomas in infants and young children. In order to maximize the probability of obtaining useful information from each eye, only relative interocular acuity differences will be measured. Monocular VEPs will be recorded with only one check size; the interocular amplitude ratio for the N1P1 and P1N2 VEP components and the interocular P1 latency difference will be measured. FPL interocular acuity estimates will be obtained using age appropriate suprathreshold diagnostic stripes.